Block ciphers are a well known family of symmetric key-based ciphers. Block ciphers operate on plain text in groups of bits. The groups of bits are referred to as blocks. Block ciphers are dealt with at length in Chapters 12-15 of Applied Cryptography, Second Edition, by Bruce Schneier, published by John Wiley and Sons, 1996. Many block ciphers are constructed by repeatedly applying a function. Such block ciphers are known as iterated block ciphers. An iteration of the block cipher is termed a round, and the repeated function is termed a round function. The number of times the round is repeated in an iterated block cipher is referred to as a round number (RN).
One block cipher, DES, is specified in FIPS 46-3, available on the Internet at: csrc.nist.gov/publications/flps/fips46-3/fips46-3.pdf. FIPS 46-3 is hereby incorporated herein by reference.
A second well known block cipher, AES, is specified in FIPS 197, available on the Internet at: csrc.nist.gov/publications/flps/fips197/fips-197.pdf. FIPS 197 is hereby incorporated herein by reference.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.